The major objective of the proposed research is to determine the advantages of binaural hearing among normal and hearing impaired individuals by exploring localization and directional hearing abilities during conditions in which the head is immobilized as contrasted to conditions in which head movement is encouraged and measured. Further investigations will determine the relationships between localization ability and speech reception when stimuli are presented in backgrounds of competition. The problem of specifying the superiority of the binaural listener (normal or hearing impaired listener) is complicated by the acoustic conditions of the environment, head movement, the acoustic shadow of the head, and the magnitude and type of hearing loss. Each of these variables will be considered within the experimental design. The proposal describes an optical method of measuring head movement which will provide quantitative measurement of latency, direction and velocity of the movement. In the experiments concerned with the relationship between localization and speech reception performance, comparisons will be made between the functional separation of the primary and competing signals (localization) and the binaural enhancement of intelligibility as manifested in observations of masking level differences (MLD) for speech. BIBLIOGRAPHIC REFERENCES: Dirks, D., Morgan D. and Wilson R. Experimental Audiology. Chapter 7 in Handbook of Auditory and Vestibular Research Methods. Edited by Vernon, J. and Smith, C. C. Charles Thomas Company, 1975. Fee, W., Dirks, D., Morgan, D. Nonacoustic Stimulation of the Middle Ear Muscle Reflex. Ann. Oto. Rhin. Laryng. 84, 80-87, 1975.